| 摘要 |
PURPOSE:To readily judge the state, under which the induction motor is shifted to the unstable region, by comparing a preset voltage and a motor voltage, and detecting the increase in the deviation voltage between both voltages. CONSTITUTION:The preset voltage of a voltage setting device 18 and the detected voltage of a potential transformer 24 are compared through a voltage converter 40. The deviation voltage between the detected voltage, i.e. the preset voltage when the motor voltage is decreased, and the motor voltage are compared with a reference value in a comparator 36 and the difference is detected. When the preset voltage is constant and the motor 10 is shifted to the unstable region, the motor voltage is largely reduced. Therefore, the following relationship is established between the preset voltage and the detected voltage. When the preset voltage the detected voltage (motor voltage)... the operation is normal. When the preset voltage is larger than the detected voltage (motor voltage)... the motor is shifted to the unstable region. Therefore, if the comparator 36 is made to output a specified output signal when the deviation voltage between the preset voltage and detected voltage exceeds the preset value, the state, under which the motor 10 is shifted to the unstable region, can be readily judged. |
